As a staple food for nearly one-half of the world's population, rice is one of world's most important foodstuffs.
Edible rice is prepared firstly by milling the seeds of the rice plant to remove the chaff. At this point, the product is called brown rice. White rice is then produced by continuing the milling process to remove the husk and the germ. The milling and polishing that converts brown rice to white rice produces a more palatable product, but significantly reduces its nutrient and vitamin content, and removes much of the dietary fibre. Milled white rice typically contains less than about 2 wt. % of dietary fibre on dry weight basis.
Dietary fibre is defined as food material, particularly plant material, that is not hydrolysed by enzymes secreted by the human digestive tract but that may be digested by microflora in gut. Plant compositions that fall within this definition include non-starch polysaccharides (NSP) such as celluloses, gums and pectin as well as lignin, resistant dextrins and resistant starches.
There are four forms of resistant starch—RS 1 (protected starch molecules trapped in the food matrix), RS2 (unswollen granules with highly crystalline regions, e.g. potato starch and green banana starch), RS3 (resistant forms of retrograded amylose or amylopectin), and RS4 (chemically modified starch), all of which may be classed as dietary fibre.
Extensive research has been carried out into the physiological effects of dietary fibre, which is associated with a number of health benefits. High fibre foods, because of their consistency, encourage mastication and stimulate the secretion of digestive juices. The soluble components of dietary fibre cause an increase in the viscosity of the stomach contents, thereby retarding gastric emptying. This then affects the rate of digestion and the uptake of nutrients and creates a feeling of satiety.
Soluble fibre has also been shown to lower selectively serum LDL cholesterol and to improve glucose metabolism and insulin response.
In the colon, dietary fibre tends to increase faecal bulking due to increased water retention and the insoluble dietary fibre reduces transit time. This is particularly important since the conversion of sterols to carcinogenic polycyclic aromatic hydrocarbons is known to occur with time. Epidemiological evidence suggests low faecal weights are associated with an increased risk of cancer of the colon. Dietary fibre may also bind toxins, bile acids and carcinogens. Inverse relationships between fibre intake and the incidence of obesity, heart disease, cancers (of the colon and breast), diabetes and gastrointestinal disorders have been reported. Dietary fibre may also be beneficial in weight reduction.
Brown rice contains a beneficial amount of dietary fibre in the bran layer. However, despite the associated health benefits of brown rice, milled white rice is still generally the more popular product. Certain characteristics of brown rice make it less appealing than white rice, including its darker colour, its longer cooking time, and its propensity to spoil more quickly than white rice due to fat-containing germ-which is removed when making white rice.
As an alternative to brown rice, a number of high-fibre products have been developed by coating processed white rice with dietary fibre.
JP 06-026507 discloses a processed polished rice processing method in which a water solution of one or more kinds of soluble dietary fibre such as guar gum, locust bean gum, tamarind gum and pectin is sprayed onto the surface of rice while it is being polished and then dried. JP 06-026507 discloses a process in which soluble dietary fibre is sprayed onto processed polished rice which is then boiled. During boiling, the soluble dietary fibre “melts” into the water and at the end of the cooking time has entered into the starch tissue of the rice. AU-A-2008335453 describes methods of coating powdered bran onto parboiled milled rice grains.
However, using coating methods to increase the fibre content has certain disadvantages. Rice is often washed with water before cooking, and during cooking is often boiled for up to half an hour. Both the washing and cooking stages can serve to remove or erode the high-fibre coating before it is consumed.
One approach to overcome the problems associated with using coatings is to prepare reconstituted rice kernels.
This approach has been used to incorporate vitamins and other nutrients into rice. FR-A-1530248 discloses fortified artificial kernels prepared from a mixture of semolina or flour and vitamins. The mixture is then formed into strands which are cut into rice-size pieces which are dried. The artificial kernels are mixed with natural grains in a 1:20 up to 1:1000 mixture. However, the artificial kernels often tend to disintegrate during cooking, thereby losing the vitamins to the cooking water and reducing the potential beneficial properties when the cooked rice is consumed.
The process disclosed in U.S. Pat. No. 5,609,896 uses extrusion to prepare artificial enriched rice kernels and overcomes the problems of cooking instability and subsequent vitamin loss by adding specific ingredients such as heat stabilising agents, binding agents and cross-linking agents. However, although the addition of these agents produces a more stable product, production times and costs are increased. Furthermore, such additives have been linked to allergenic reactions and have even been cited as being possible carcinogens.
WO-A-2005053433 describes processes for the preparation of enriched rice-like grains by extrusion of a mixture of rice flour or broken rice with water, one or more micronutrients such as vitamins, and an emulsifier, followed by drying. Similar products and processes are described in WO-A-2010/020640.
KR-A-20060120335 describes processes for the preparation of rice-like grains by extruding a mixture of rice flour and resistant starch, followed by drying. Fabricated rice-like grains are also described in U.S. Pat. No. 4,886,675, EP-A-1166648, EP-A-0277498 and U.S. Pat. No. 5,932,271.
W02010/102521 describes forming reconstituted cereal grains from a multi-grain raw material that is ground and mixed with water, an emulsifier and further ingredients such as cellulose and nutrients, prior to extrusion.
CN-A-101869241 describes extruded cereal grains based on vanous kinds of flour, including rice flour, pearl barley, red bean or green bean flour. The grains may contain 0-12% of cellulose.
US 2004/109931 describes a reconstituted cereal grain formed from a dough that may contain 1-10% by weight (dry weight) of rice bran.
A need remains for providing an enhanced-fibre granular product which retains its stability and fibre-content whilst being washed and cooked, and also provide a palatable taste and texture when eaten. Preferably, the enhanced-fibre granular product is made via an inexpensive and simple process.